# RefDateTime.subtractDuration

Subtract a Duration from the current state of a RefDateTime.

## Signatures

```ts
export declare const subtractDuration: {
    (duration: Duration.Input): <E, R>(ref: RefDateTime<E, R>) => RefSubject.Computed<DateTime.DateTime, E, R>;
    <E, R>(ref: RefDateTime<E, R>, duration: Duration.Input): RefSubject.Computed<DateTime.DateTime, E, R>;
};
```

## Why

Subtract a Duration from the current state of a RefDateTime. The operation remains attached to
the RefSubject's versioned state boundary.

## Ownership and lifetime

The subtract duration view retains no independent state. An Effect read samples the source once;
Fx observation follows later pushes and its observing Scope owns subscription cleanup.